Color television



Sept 1943- A. H. ROSENTHAL 2,330,172

COLOR TELEVIS ION Filed April 8, 1959 2 Sheets-Sheet l p 1943: A. H. ROSENTHAL 2,330,172

COLOR TELEVISION Filed April 8, 1959 2 Sheets-Sheet 2 Patented Sept. 21 1943 'FFICE 2,330,172 coLon'mLEwsroN Adolph Henry. Rosenthal, New York, N. Y.', assignor, by mesne assignments, to Scophony Cornotation of America, New York, N. Y., a corporation of Delaware Application April 8, 1939, Serial No. 266,876 In Great Britain. April 12, 1938 13!. Claims.

The present invention relates to systems for the productionof television pictures in natural colors.

There have been many proposals for utilizing the so -called additive method of color reproduction in televisionsystems In this system the final colored picture is obtained by superimposing a pluralityof partial images, the color of each partial, image being one of the so-called primary colors of the particular color process employed. This process is usually a three color process employing certain red, green and blue colors as the primary colors, but other color processes such as a two color process have been proposed. The superposition of the partial images can be efiected simultaneously or successively, and they can be projected one on top of the other, or the corresponding elements or lines of the partial images can be placed side by side or interleaved respectively.

The use of additive methods possesses the serious disadvantage that the light efliciency is poor. In the average only a small part of the incident white light is utilized in forming the color picture; for. example in a three color system only one-third of the incident light is utilized.

In color photography an alternative method,

known as' the subtractive method is used. In this system the color values'are derived from the incident white light by the successive subtrac the subtractive method. This is achieved by deriving from a transmitter by any known or suitable color separation method sets of modulated signals each representative of the intensity of one of the primary colors of the object to be transmitted, utilizing each of these sets at the receiver to produce a corresponding fugitive col-.-

1 or deposit in a transparent screen, the color of tion of certain portions thereof, by passing the light in succession through transparencies, each of which contains a record of one partial image in the form of a deposit having a color which is complementary to the'primary color of, and a transparency proportional to the intensity of the partial image in question. Thus if a three color process based on red, green and blue as the primary colors is employed, the complementary color deposits in the three respective transparencies would be bluish green (minus red), magenta (minus green) and yellow (minus blue) respectively. At points corresponding to white in the final color picture each transparency is free from any color deposit so that the whole of the white light incident at this point passes'through all the transparencies without substantial loss.

To produce a color picture by the subtractive method having the same brightness as a picture produced by the additive method only a fraction of the illuminating light is necessary, for example one third in the case of a three color system.

According to the present invention there is provided a color television system which employs screens of theionic crystal material type described in co-pending application .No. 253,182.

If certain crystals, which are normally transparent to visible light, are struck by a beam of cathode rays, X-rays, radium rays, orby'light' of a suitable wave length, a deposit of opaque material, which is constituted by what will hereinafter be referred to as opacity centres, is created in this crystahthe degree of opacity depending on the intensity of the incident radiation Examples of such crystals are many of the alkali and alkaline earth halides, such as the chlorides, bromides and iodides of sodium and potassium, lithium bromide, calcium fluoride, and strontium fluoride and chloride; and also certain silver salts such as silver bromide. In the case of the alkali halide crystals research has indicated that the opacity centres probably consist of neutral alkali atoms which are loosely bound in the interior of the crystals in some manner or other, and which are similar to the deposit of metallic silver in a latent photographic image The deposit of metal in the crystal lattice can also be created by heating an alkali halide crystal in an atmosphere of the vapor of its alkali metal, which difiuses into the crystal.

Once formed, the opaque deposit can also be destroyed by the above mentioned rays, the amount of destruction in a given time interval depending on the intensity of the rays and on the density of the deposit already formed. Thus the gross efiect of any given intensity of the incident radiation, being the result of an equilibrium between the formation and destruction of the deposit, may be an increase of the deposit for low intensities and a decrease for the high intensities, in a manner similar to the well known solarisation of the latent photographic image. Thus,-

over a range of low intensities of the incident ra diation, increase in intensity will result in an increase of the deposit, whilst over a range of high intensities an increase in intensity will result in a decrease of the deposit.

The materials exhibiting this property maybe defined as ionic crystals in which the injection of electrons into the crystal lattice can produce an opaque deposit which can be moved within the crystal lattice by application of electric fields and heat.

In the co-pending application referred to above there is contemplated the use of a transparent crystalline material of the type defined in the image screen of a television receiver. The materialmay be in the form of a single fiat crystal, a mosaic of small crystals, or a micro-crystalline structure. A composite crystal or a mixture of the two or more of such crystalline materials may be used.

In most cases, and particularly when the material is in the form-of a single crystal, a disappearance of the opaque deposit can be produced by maintaining the crystal in an electric field and at a suitable temperature, in which case thedeposit is drawn through the crystal towards the positive pole producing the electric field. When it reaches the positive pole it disappears, leaving the crystal substantially transparent. The speed of movement of the deposit depends upon the strength of the field and upon the temperature, and can be varied within wide limits by varying either magnitude. For a given field strength this speed of movement increases with the temperature of the crystal.

The spectral transmission of these colored de-- posits is different for different materials, and can also be varied by changing the temperature. Thus for a given alkali'halide crystal the spectral absorption curves get broader and the region of maximum absorption is shifted towards the longer wave-lengths with increase of temperature. Thus by a suitable choice of material and/or operating temperature screens having deposits of the colors necessary for any color process can be obtained. For example in a three color process based on red, green and blue as the primary colors, suitable materials for the therein, are only shown diagrammatically in the present application. Means indicated at I3, I4, I5

are associated with the tubes for producing a scanning cathode ray beam, and amplifying arrangement I6 by signals representative of one of the-primary colors'of the object being transmitthree screens are the following alkali halide I crystals: KBr, KI, RbCl, RbBr, for the minus red deposit. KCi, NaBr for the minus green' deposit and NaCl, LiCi, KF for the minus-blue deposit. 4

A preferred embodiment of the invention as applied to a television receiver intended to reproduce colored pictures according to a three color process will now be described; by way of example with reference to theraccompanying drawings in which Figs. 1 and 2 show diagrammatically two alternative arrangements according to the present invention.

Referring to Fig. 1, three cathode raytubes I,

2 and 3 are provided, each comprising a transparent image screen indicated at 4, 5 and 6 respectively. Each screen is situated in an elec"- tric field provided by pair of transparent electrodes I, 8 and 9, across which is maintained a potential difference by means of a source of the amount of the-current and hence the tem-' ted. The sense of the modulations applied to the beam is such that the density of the deposit produced is inversely proportional to the intensity of the corresponding primary color. The v three beams are caused to traverse the three screens 4. 5 and Ii in synchronism by means of scanning coils I3a, Ma, and I 5a.

The material and/or temperature of the screens are chosenso that the colored deposits produced therein have the required complementary colors. White light from a suitable source I! is projected successively through the three screens 4, 5 and 6 in such a way that the .screen images are superimposed in register on a reproduction surface I8. This can be done by fully illuminating the first screen with a condenser system I9 which also forms an image of the light source H on a first projection lens 20 situated between the first two screens 4 and 5. This projection lens 20 forms an image of the first screen 4 on the second screen 5 inregister, and the light is focussed by means of a field lens 2| on to a second projection lens 22 which forms an image of the second screen B'on the third screen Bin register. ,A field lens 23 focusses the light passing through the screen, 6 into a final projection lens 24 which forms an image of the third screen 6 on the reproduction surface I8, forming thereon the final colorpicture.

It will be noted that with the inverting optical system. shown the image on the screen 4 must be inverted, that on screen 5 upright and that on screen 6 inverted, so that the projection lens 24 forms an upright image of the screen I8. This can be arranged by applying the deflecting currents to the coils I30, I la. and Ilia in a suitable sense.

An alternative arrangement is shown in Fig. 2, in which parts similar to those of Fig. 1 are given the same reference numerals. The first screen 4 in the tubeI is the same as that shown in Fig. 1. In place of the two tubes 2 and I of Fig. 1 there is used in the arrangement of Fig. 2 a single tube 25 having two cathode ray guns I4 and I5, and a double screen which is composed of two screens 26 and 2 1 separated by a common transparent positive electrode 28 and having on their outer surfaces transparent negative electrodes 28 and 30 respectively. Thus electrical fields are maintained in the screens in such a way that the color deposits in the two screens will move towards each other and disappear at the common electrode. The beam from'the gun I4 produces in the screen 26 an image corresponding to the image on the screen 5 of Fig. l, and the beam from the gun I5 produces in the screen 21 an image corresponding to the image on the screen 6 of Fig. 1. A lens 3| forms an image of the screen 4 on the composite screen 26, 21, and the projection lens 24 acting in conjunction with a collecting lens 32 forms the final image on the projection screen I8. In a three color process the tube 25 would p turepe we users; It is necessary to transmit more than 50 partial images per second in order to avoid flickering at high intensities.

In the present system in which complete storage of the partial images over the picture period are possible a picture repetition frequency of 17-20 per second is completely satisfactory, and hence the total width of the frequency band necessary to transmit the signals is no greater than that required to transmit the signals representing a black-and-white picture by methods in which no storage of the received picture takes place.

I claim: I

1. Television receiving apparatus for the reproduction of colored objects, said apparatus comprising means for receiving N sets of transmitted signals each representative of one of the N color components of the object to be transmitted, N transparent screens each corresponding to one of said sets of signals and each screen including a layer of an alkali halide, means for scanning each of said N screens with a cathode ray beam, means for modulating the N cathode ray beams each with the corresponding set of received signals,said alkali halides being of such nature and being held at such a temperature that as a result of said scanning there is produced in each screen an image in a color which is complementary to the color of the corresponding transmitted color component, the density of said image being inversely proportional to the intensity of said color component, means for rendering said image fugitive within the frame scanning period and optical means for projecting a light beam through said screens to form a composite color image of the transmitted object.

2. Television receiving apparatus for reproduction of colored pictures comprising a plurality of cathode ray tubes, each tube being controlled by a transmitted color component of the original picture, a screen surface on each of said cathode ray tubes adapted to be scanned by an electron beam produced in each of said cathode ray tubes, said screen being composed of a material which when subjected to electronic bombardment has a color complementary to the color of the corresponding component of. the original picture, said material being normally transparent when not subjected to electronic bombardment, the intensity of the color of any elemental area of said surface being proportionate to the intensity of .electronicbombardment, means for modulating said cathode ray beam inversely proportionate to the color intensity of said component of the original picture, a source of light and means for viewing a complete image, said cathode ray tubes being. positioned between said source oi light and said viewing means in such a manner '1 is 5.3;"; nan.

6. A television receiving ap aratus of the t described in claim '2 wherein said screen comprises a transparent alkali halide layer between a pair of transparent electrodes adapted to create a potential difierence across the alkali halide layer.

I 7. A television receiving apparatus of. the type described in claim 2 wherein said screen comprises a transparent alkali halide layer between a pair of transparent electrodes adapted to create a potential diiference across the alkali halide layer, and a means for controlling the temperature of said alkali halide layer. v I

8. A television receiving apparatus of the t described in claim 2 wherein said screen comprises a transparent alkali halide layer between a pair of transparent electrodes adapted to create a potential difierence across the alkali halide layer, and a means for controlling the temperature of said alkali halide layer, said means comprising a source of current in circuit with one of said transparent electrodes and a thermostat controlled by the temperature of said alkali halide layer controlling the amount of current flowing through said electrode from said source of current in accordance with the temperature of said alkali halide layer.

9. A television receiving apparatus of the type of an alkali halide from the group consisting of sodium chloride, lithium chloride and potassium fluoride.

10. Television receiving apparatus for the reproduction of colored objects, said apparatus comprising means for receiving N setsv of transmitted signals each representative of one of the N colored components of the object to be transmitted, N screens each corresponding to one of said sets of signals and each screen including a layer of an ionic crystal material, means for scanning each of said N screens with a radiant beam, means for modulating the N radiant beams each with the corresponding set of received signals, said crystal materials respectively being of such nature that said scanning will produce in each screen an image in .a color which is complementary to the color of the corresponding transmitted color component, the density of said image being inversely proportional to the intensity ofsaid color component, means {for render-- and the various color components or thelight layers being or a different ionic crystal mate rial, all or ,the materials being such that colored areas movable between said faces may be created therein by a radiant beam, but said materialsrespectively being such that the colored areas created in each will be complementary to a diflerent primary color,a scanning means for each. layer, means to control each scanning 'means in accordance with the intensity oi! a primary color in the object and to modulate said scanning means to an intensity inversely proportional to the intensity of that primary color in the object to thereby create colored areas in the complementary color in successive elemental 1 portions of the layers, and means to restore said layers to their normal light transmitting characteristics within a predetermined time period.

. ADOLPH HENRY ROSENTHAL. 

